This invention relates to inference of vehicular trajectory characteristics with mobile computing devices, and in particular to inference of vehicular acceleration and velocity using commodity devices such as smartphones. The acceleration computed includes a longitudinal component in the principal direction of movement of the vehicle, and may be positive, zero, or negative (indicating deceleration), as well as a lateral component perpendicular to the longitudinal in the plane of movement. A noteworthy aspect of the invention is that it uses raw sensor data from a mobile device that is not in a known or fixed orientation in the vehicle, and allows the orientation and placement to change from time to time. The invention is battery-efficient and well-suited for battery-efficient operation on personal mobile devices such as smartphones.
Inference of characteristics of a vehicle's trajectory, including velocity and acceleration, has previously been addressed using inertial measurement and positioning systems. With inertial systems, accelerometers (e.g., one or multiple axis or degree of freedom linear and/or rotational accelerometers) that are rigidly placed or fastened to the vehicle in a known position and orientation have been used to determine velocity by numerically integrating acceleration signals. Positioning systems, such as the Global Positioning System (GPS), have been used to infer velocity. Integration of accelerometer signals may have technical limitations, for example, related to “drift” whereby a velocity or position estimate may have progressively increasing error. Inference of velocity characteristics using a positioning system may have technical limitations such that inference or detection of acceleration or rapid changes in velocity may be impossible because the reported velocity estimates may be smoothed, preventing sudden acceleration and deceleration events from being inferred.
Personal mobile devices, for example, smartphones, personal digital assistants, and the like may have integrated accelerometers and positioning system receivers. Use of such devices for inference of a vehicle's trajectory may have limitations, for example, related to an uncontrolled, unpredictable, and changing placement and orientation of the device relative to the vehicle, and related to high power consumption required for frequent acquisition of position estimates from a positioning system, particularly GPS.